User equipment (UE), also known as mobile stations, wireless terminals and/or mobile terminals are enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The communication may be made e.g. between two user equipment units, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks.
The user equipment units may further be referred to as mobile telephones, cellular telephones, e-readers, laptops with wireless capability etc. The user equipment units in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data wirelessly, via the radio access network, with another entity, such as another user equipment or a server.
The wireless communication system covers a geographical area which is divided into cell areas, with each cell area being served by a network node, or base station e.g. a Radio Base Station (RBS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the network node/base station at a base station site. One base station, situated on the base station site, may serve one or several cells. The network nodes communicate over the air interface operating on radio frequencies with the user equipment units within range of the respective network node.
In some radio access networks, several network nodes may be connected, e.g. by landlines or microwave, to a Radio Network Controller (RNC) e.g. in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural network nodes connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes, or base stations, which may be referred to as eNodeBs or even eNBs, may be connected to the core network directly or e.g. via a gateway such as e.g. a radio access gateway. The gateway may in turn be connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
The 3GPP is responsible for the standardization of GSM, UMTS and LTE. LTE is a technology for realizing high-speed packet-based communication that may reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative UMTS.
In the present context, the expression downlink is used for the transmission path from the network node to the user equipment. In some literature, the transmission path from the network node to the user equipment may sometimes be referred to as downstream, or forward link. The expression uplink is used for the transmission path in the opposite direction i.e. from the user equipment to the network node. This is sometimes referred to as upstream or backward link.
Coordinated Multipoint transmission and reception (CoMP) is considered a feature that may enhance the performance of mobile radio networks/wireless communication systems. In short, when using coordinated multipoint cells that normally operate independently are formed into cooperating groups and transmissions and receptions within this group of cells are coordinated. In the downlink, the coordination may be implemented as, e.g., coordinated scheduling, coordinated beam forming or coordinated joint processing. In the uplink, the cells within the coordination area may be used as a large antenna array (with well separated antenna elements), which improves the receive diversity and interference suppression capabilities.
To take full advantage of the coordination, coordinated multipoint cells may be grouped such that cells within the group have a large mutual dependence whereas cells in different groups have a low dependence. The potential performance gains of coordinated multipoint cells may typically increase with the size of the coordinated cell. However, real-world constraints such as e.g. transport network capacity and delays, signal processing capabilities and complexity limits the practical size of the coordinated multipoint cells.
In scenarios where the environment, deployment, and traffic is homogeneous a way of forming coordination areas for coordinating cells may be to group cells together based on that the cells are geographically close. Such a method may, however, not be very well suited in a case where the environment, the deployment or the traffic is heterogeneous and/or is time variant.
The previously known methods of forming CoMP cells suffer from a plurality of problems, such as for example that they presupposes a centralized processing unit, they concern static or semi-static coordinated multipoint cell group selection based on statistics and are thereby not suitable for dynamic adaptation to changed radio propagation conditions, and that they does not change the overall coordinated multipoint cell group composition, rather captures subset operation on a per user equipment base.
The question of adapting the coordinated multipoint cell group members dynamically is however important in order to have an efficient utilization of the increased complexity introduced in the network. The formation of a coordinated multipoint cell implies an increased level of hardware processing and backhaul capacity than what is the case in traditionally deployed networks that are uncoordinated. Due to the inherent trade-off between increased number of included cells (typically more cells gives improved performance) and increased complexity, a foreseeable problem of forming coordinated multipoint cell groups is under utilization. That is, groups of cells that do not show capacity or coverage performance as expected from their size while other cells, not members in the group, may have contributed more positively for the same complexity.
Deployments may change, e.g., since new cells are added and some cells may be removed. Furthermore, cells may be turned on/off by Radio Resource Management (RRM) algorithms, e.g., to optimize energy usage of the network node. Traffic patterns may change, e.g. over the day; high/low traffic, geographically; home/office, etc. In an environment with changing deployments and changing traffic, there is a need for improved methods beyond the centralized methods in the prior art to act and update the coordinated multipoint cell group members on the actual experienced deployment.